The present invention relates to an improved energy saving process for the manufacture of synthetic ammonia.
The ammonia synthesis feed gas produced by conventional hydrocarbon conversion processes contains objectionable quantities of carbon dioxide and water which adversely affect the ammonia conversion catalyst. The carbon dioxide content of the raw feed gas after reforming and shifting, is reduced by conventional alkaline or solvent scrubbing, but low level residual carbon dioxide after methanation, is still objectionable in the synthesis loop.
The conventional ammonia plant removes the remaining carbon dioxide and the water from the make-up gas by introducing the make-up gas into the ammonia loop after the catalytic synthesis converter and before the refrigerating system that condenses the product ammonia. The liquefying ammonia absorbs the carbon dioxide and water from the unreacted synthesis gas which is then recommended with recycled gas and passed to the converter.
It has also been proposed to remove water and residual carbon dioxide from the make-up gas by scrubbing with liquid ammonia as described for example in the patent to Nebgen, U.S. Pat. No. 3,349,569, or by using molecular sieve driers.